1. Field of the Invention
The present invention relates to open-end spinning, i.e. rotor spinning.
2. Description of Related Art
Open-end spinning frames normally consist of a series of individual spinning units, aligned on the two fronts of the machine, each of which consists of a spinning rotor, which produces heald yarn starting from the single fibers of a sliver and from a collecting unit which—after controlling the quality of the yarn by interposing a slit plate between the two components—leads the yarn to wind on a winding tube to produce a tapered bobbin. This tapered bobbin is formed by pulling and winding the yarn on its surface, as it is rotated by the underlying roll on which the bobbin in formation rests. The yarn is wound in cross-coils on the rotating tapered bobbin, as the collecting unit is equipped with a yarn carrier which distributes the yarn, by means of an axial backward-and-forward movement, on the external surface of the tapered bobbin.
The structure of the individual spinning station is shown in the scheme of FIG. 1, and its functioning is briefly described hereunder according to its normal operating conditions.
Proceeding from below upwards, the spinning station 1 consists of the actual spinning unit 2, and the collecting unit 3, whose main components are briefly described hereunder, which transform the sliver with parallel fibres into yarn wound onto the tapered bobbin.
The feeding sliver S is housed in a cylindrical container 4 where it is deposited in a double spiral. The sliver S is fed to the unit by a feeding roll 5, passing through the funnel conveyor 6 and reaches the card 7, a rotating roll equipped with a clothing which makes the fibres of the sliver S singular and sends them, by suction, to the spinning rotor 8, which operates under depression.
The singularised fibers are deposited, by centrifugal effect, on the peripheral throat of the spinning rotor 8, which rotates at extremely high rates (up to 150,000 rev/minute and over); from here the fibers are collected and removed as a yarn F, axially leaving the central opening 9, receiving torsions from the rotation of the rotor itself, during the run between its inner throat and said opening 9, thus generating the twisted yarn F.
The withdrawal of the yarn is effected by a pair of opposing extraction cylinders 11 and 12, which seize the yarn F and operating at a controlled rate, according to the arrow a, thus determining the linear production of the yarn, normally expressed as m/min. The slit plate 14 for the control of the yarn F quality can be situated before the cylinders 11/12.
The yarn F thus produced enters the collecting unit 3, passes through a sensor 15 detecting the presence of the yarn and reaches a compensator 16 to compensate the length variations of the distance between the spinning unit 2 and the deposition point of the yarn F on the tapered bobbin. The yarn-carrier device 21 distributes the yarn on the tapered bobbin by transversally moving with a backward-and-forward motion according to the double arrow b, driven by a motor 20 which operates a longitudinal rod 22 in common with the other units of the spinning frame.
The tapered bobbin 25 collects the yarn F and is held by the bobbin-holder arm 26 equipped with two idle and openable counter-spikes 27, which are connected to the base tube 28 of the tapered bobbin. The tapered bobbin in formation 25 rests against its operating roll or collecting cylinder 29.
The automatic open-end spinning frames of a recent design are equipped with service trolleys which inspect the front lines of the spinning frame and automatically effect the necessary interventions stopping in front of the spinning unit which requires them.
There are essentially three types of required interventions:                starting operation, at the beginning of the spinning, when the spinning frame is still, starting it and subsequently placing a new yarning tube in each station, the start-up being effected by re-attachment with an auxiliary yarn and winding the yarn produced on the new tube, to give a tapered bobbin, after eliminating the section of auxiliary yarn;        re-attachment, when the yarn is interrupted for any reason, before reaching the envisaged length for completing the tapered bobbin, using the yarn already produced at the side of the tapered bobbin, effecting the re-attachment and restarting the winding on the same tapered bobbin. The re-attachment procedure consists, in its essential lines, in the opening, cleaning and closing of the rotor, in the preparation of the tail of the sliver, the capture and preparation of the end, at the side of the tapered bobbin, the re-starting of the rotor and feeding, the re-introduction in the rotor of the prepared end, the re-extraction of the end connected to the newly produced yarn, by winding it again in the collecting unit. The programmed cleaning cycle is equivalent to the re-attachment cycle, caused by a specific breakage of the yarn;        collecting, after reaching the desired length to complete the tapered bobbin. The finished tapered bobbin is discharged and the unit is then restarted as specified above.        
These interventions of the controlling trolleys relate to both the collecting and starting or re-starting operations of the spinning station and to the repairing of yarn cuts due to natural causes or operated by the slit plates during the spinning.
In general, these interventions are effected by separating the tapered bobbin 25 from its operating cylinder 29, halting its movement and substituting the driving of the tapered bobbin 25 or its tube 28 by an auxiliary driving roll, positioned inside a service trolley.
In the field of devices and intervention procedures of service trolleys in automated open-end spinning frames, the Applicant owns, among others, the recent European patent applications nr. 04077813.6, 04077814.4, 040778818.5, 04077819.3, as well as patents EP 340,863, EP 443,220, EP 473,212.
Reference is made to these known technique references for greater details on the structure and functioning of these service trolleys.
A device and re-attachment procedure for obtaining—in said transitory phases—a yarn having good mechanical and aesthetical characteristics, is described in the previous European patent application 04077818.5. For the sake of brevity, reference should be made to this document, in which the whole trolley is described in great detail with respect to its components.
The intervention procedures carried out by service trolleys consist of a relevant number of phases effected from the trolley, interfacing it to the single unit or open-end spinning station with both its spinning rotor and overlying collecting unit, temporarily disconnecting these organs from their centralized driving units, and operating on the same with their own driving units, capable of bringing the spinning back to regime conditions, before re-activating the centralized commands and reconsigning the spinning unit to its normal centralized driving.
In the open-end technology, the main problem of high quality tapered bobbin winding, derives from the fact that the open-end yarn is produced and delivered to the collecting unit intrinsically at a constant linear rate with a collecting system and that the yarn tension must in any case, also during transitory phases, be controlled and maintained within pre-established ranges.
In a open-end spinning frame, the extraction rate of the yarn from the spinning rotor with extraction rolls or cylinders 11,12, is strictly constant—apart from the short re-attachment transitory—as is also the collecting rate. Considering that the driving units are in common and centralized and that differences can exist between units, either as a result of different advancement degrees of the tapered bobbin during production, or due to small geometrical or set-up differences between the spinning units, the open-end machine normally operates with a slight predominance of the collecting rate with respect to the yarn extraction rate, exploiting the elasticity of the yarn, thus generating a certain “reeling” tension: this rate difference is an adjustable parameter of the machine according to the operative conditions and has a value of a few units per thousand. This expedient is due to the requirement that a loosening of the yarn downstream of the extraction rolls 11,12 is not acceptable, otherwise causing problems of yarn control and the impossibility of forming a tapered bobbin having the required characteristics for its use, downstream of the spinning process.
Once the re-attachment has been successfully effected, the control and recovery phase of the yarn on the tapered bobbin 25 is of great importance, together with the re-consignment of the tapered bobbin itself from the auxiliary driving device situated in the service trolley to its normal driving roll 29 under regime conditions, which is part of the open-end spinning unit.